I have a Boss Therm BPS242RF thermostat and Boss Therm BR1 receiver and Glowworm Betacom 24.
My boiler CH is not working, hot water is OK, I have gone through the pairing process with the boiler switched off.
1. Pressed and held SET and a RESET buttons for 4 seconds
2. Pressed and held RESET button for 2 seconds
3. With the back plate on thermostat removed pressed and held LEARN button for 2 seconds
4. Turned boiler back on
5. Timer toggle switch will not stay on CONSTANT setting

michael rabbatts, November 2022